This thesis is concerned with a variety of topics grouped together under the general theme of periodically driven atomic systems. Periodic driving is ubiquitous in most techniques used in atomic physics, be it laser cooling, ion trapping or AC magnetic fields. An in-depth understanding of the behaviour of such systems can be provided through Floquet theory which will develop as a central theme in the following chapters. The thesis is divided in two parts: neutral atoms, and ions and biomolecules. In the first part I discuss a new ⁴¹K-⁸⁷Rb mixture experiment, built during the first year of my DPhil. This species combination has some very broad and low-loss interspecies Feshbach resonances that are instrumental for carrying out the experiments discussed in the first chapter. Unfortunately, the mixture experiment had to be put aside and our attention was shifted to Time-Averaged Adiabatic Potentials (TAAPs) and how these can be extended using multiple Radio-Frequency (RF) fields. This technique opens up the way for precise interferometric measurements. Lastly, the peculiar behaviour of Modulation Transfer Spectroscopy (MTS) of ³⁹K is investigated and a linearising transformation for four-wave mixing processes is presented. In the second part we turn our attention to charged ions and biomolecules and the techniques of ion trapping. We propose a novel technique for co-trapping charged particles with vastly different mass-to-charge ratios and thoroughly explore its consequences. The behaviour of the trap and the stability of equations with periodic coefficients in general is studied using Floquet theory. The normal modes and symmetries of the system also need to be considered in relation to the effectiveness of the sympathetic cooling of the ions. Small systems were simulated using a Molecular Dynamics (MD) approach in order to capture the effect of micromotion and other heating processes.

This thesis describes the construction of an Optical Tweezer apparatus to be used in conjunction with a confocal Raman spectrometer. The tweezer utilizes an infrared (λ=1064 nm) laser directed into an inverted microscope with NA=1.4 oil immersion 100x objective lens that strongly focuses the laser light into a sample to function as a single-beam gradient force trap. The long term goal of this research program is to develop a single molecule Raman tweezers apparatus that allows one to control the position of a Raman nanoplasmonic amplifier. This thesis describes the construction of the Raman tweezer apparatus along with several Raman spectra obtained from optically trapped samples of polystyrene fluorescent orange, amine-modified latex beads. In addition, I explored the Raman spectra of bulk cytochrome c mixed with or injected onto Ag aggregates for SERs enhancement.

Le Nitrure de Gallium est devenu un matériau incontournable pour le développement de dispositifs semi-conducteurs aux performances très supérieures aux composants silicium. L'immense potentiel du dispositif HEMT AlGaN / GaN provient du gaz d'électrons à haute densité et à forte mobilité formé au niveau de son hétéro-structure. Cependant, le fonctionnement sous champ électrique, température et conditions de stress élevés rend le dispositif vulnérable aux problèmes de fiabilité qui limitent son efficacité et sa durée de vie. Les pièges présents dans la structure, qui limitent la densité porteurs du canal et pénalisent la réponse du dispositif, constituent le facteur majeur déterminant plusieurs effets électriques parasites et la fiabilité du dispositif. L’industrie du GaN est confrontée à la nécessité de disposer de dispositifs de haute fiabilité si bien qu’il est nécessaire de faire des progrès dans l’analyse de l’impact des pièges pour en déduire des solutions technologiques permettant leur inhibition.La motivation de ce travail est d’identifier les signatures électriques associées à l’activité de différents pièges ainsi que leurs conséquences sur les performances et la fiabilité des HEMT GaN grâce à une étude dédiée des dispositifs de la technologie GH-25 conçue pour des applications RF de puissance fonctionnant jusqu’à 20 GHz. L’étude utilise des simulations physiques TCAD. Une analyse détaillée des effets indépendants et interdépendants est réalisée afin d'identifier l'impact relatif des pièges pour des études de cas où les caractéristiques électriques présentent des écarts importants par rapport à la réponse idéale du dispositif.La méthodologie utilisée pour développer un modèle TCAD représentatif et dérivé de la physique interne est décrite en accordant une attention particulière au courant de fuite de grille qui reflète l'influence de processus physiques fondamentaux ainsi que les effets parasites couramment rencontrés dans les dispositifs GaN. Les simulations ciblées établissent un lien entre l'observation d'un problème de fiabilité et son origine sous-jacente dans les phénomènes de piégeage.L’établissement d’associations entre la localisation spatiale des pièges et les dégradations qu’ils pourraient provoquer est un objectif important de cette thèse.Plusieurs stratégies de simulation sont présentées, permettant d’explorer le comportement des pièges en régime permanent et en régime transitoire et donnant une perception détaillée de la manière dont les paramètres des pièges affectent les caractéristiques opérationnelles. Des approches pour distinguer les interactions de pièges différents sont également décrites. L’étude centrale de cette thèse est un phénomène de courant de fuite parasite complexe, identifié dans le procédé GH 25comme conséquence du vieillissement accéléré. Connu sous le nom de «belly-shape», il représente un exemple intéressant de la façon dont les stratégies développées peuvent être appliquées pour discerner la causalité, l'impact et l'évolution des pièges responsables du phénomène. Afin d'approfondir l'analyse des modes de piégeage, nous avons procédé à des tests de vieillissement accéléré et des caractérisations électro-optiques afin de modifier la dynamique générale du mécanisme de piégeage et d'observer la modulation du mécanisme du piégeage sur la réponse du dispositif. / Gallium Nitride has emerged as a terrific contender to lead the future of the semiconductor industry beyond the performance limits of silicon.The immense potential of the AlGaN/GaN HEMT device is derived from the high density, high mobility electron gas formed at its hetero-structure. However, frequent subjection to high electric field, temperature and stress conditions makes the device vulnerable to reliability issues that restrict its efficiency and life time. A dominant contributor to several parasitic and reliability issues are traps present within the semiconductor structure which restrict the channel density and aggravate the device static and dynamic response. As the GaN industry addresses an increasing demand for superior devices, reliability analysis is of critical importance. There is a necessity to enable advancements in trap inhibition which would allow the realization of stronger, efficient devices.The motivation of this work is to recognize distinct ways in which various traps affect the performance and reliability metrics of GaN 0.25 µm HEMTs through a study of devices of the GH-25 process optimized for high power applications up to 20 GHz. The investigation employs physical TCAD simulations to provide insight and perspective to electrical and optical characterizations. Detailed analysis into independent and interrelated effects is performed to identify the relative impact of traps in circumstances presenting notable deviations from the ideal device response.The methodology to develop a representative TCAD model derived closely from internal physics is described with special focus on the sensitive gate leakage characteristic which reflects the influence of fundamental physical processes as well as parasitic effects commonly encountered in GaN HEMTs. Targeted simulations provide a pivotal link between the observation of a reliability issue and its underlying origin in trapping phenomena. Establishing associations between the spatial location of traps and the degradations they could trigger is an important objective of this thesis.Several simulation strategies that explore trapping behavior in various steady state and transient environments are discussed which allow detailed perception into the manner and extent to which trap attributes affect operational considerations. Approaches to distinguish disparate trap interactions are also described. The central case study in this thesis is an abstruse parasitic leakage phenomenon, identified in the GH 25 process as a consequence of aging stress. Referred to as the “belly shape”, it presents an interesting example of how the developed strategies can be applied to discern the causality, impact and evolution of the responsible traps. In order to take a deeper look into trapping modes, further aging and LASER characterizations are performed to alter the general occupational dynamics and observe the modulation of trap control over device response.

Les transistors à base de nitrure de gallium (GaN) ont, de par leurs propriétés physiques, des performances inégalables par les technologies classiques à base de silicium pour l’amplification de puissance hyperfréquence. Cependant, cette technologie souffre d’effets mémoires basses fréquences inhérents aux défauts présents dans la structure du transistor : les effets de pièges. La première partie de cette thèse vise à caractériser et modéliser les effets de pièges. La séparation des effets de pièges ayant des constantes de temps courtes (quelques ms) à ceux ayant des constantes de temps longues (quelques s) a été montrée à travers des mesures I-V impulsionnelles spécifiques. Un nouveau modèle électrique, basé sur la physique, a été développé au sein d’un simulateur CAO pour prendre en compte les effets de pièges lents. Ce modèle, une fois greffé à un modèle de transistor GaN déjà existant, est validé par comparaison avec des mesures en régime grand signal. La deuxième partie de cette thèse traite la conception d’une architecture d’amplificateur reconfigurable en fréquence et en puissance pour une application E/R aéroportée. Un démonstrateur a été réalisé avec des transistors GaN sur circuit imprimé à 10 GHz. Les mesures grand signal de cet amplificateur ont démontré la reconfigurabilité de l’architecture d’amplificateur équilibré à charge modulée (LMBA). Par ailleurs, deux amplificateurs de puissance GaN ont été conçus pour servir de briques de base à une version intégrée (MMIC) de l’architecture bi-mode : un forte puissance bande X (employant un combineur de puissance innovant) et un moyenne puissance bande C à X. / GaN based High Electron Mobility Transistors (HEMT) present outstanding performances for microwave power amplification with respect to their silicon-based counterparts. However, this technology still suffers from low frequency memory effects originated from defaults in the structure, the so-called trapping effects. First part of this thesis aims to characterize and model the trapping effects. It has been shown that the slow-rate trapping effects could be separated from the fast-rate ones, by carrying specific pulsed I-V measurements. Consequently, a new, physic based, electrical model has been developed in order to take into account the slow traps. This model, added into an already existing GaN CAD model, has been validated through large signal measurements. Secondly, the thesis goal is to design a reconfigurable power amplifier architecture between a high power X band mode and a medium power C to X band mode for airborne T/R modules. A 10 GHz, encapsulated GaN transistors based PCB demonstrator has been realized in order to demonstrate both the power and the frequency bandwidth reconfigurability of the Load Modulated Balanced Amplifier (LMBA) architecture. Moreover, two GaN integrated power amplifiers have been designed in order to be reused in a full MMIC version of the architecture.

Neste trabalho apresentamos a construção de uma armadilha de dipolo com laser de CO2 que envolveu a utilização de novas e modernas tecnologias nunca utilizadas pelo nosso grupo até então. Podemos destacar a construção de uma nova câmara de aprisionamento com grande acesso óptico, getters como fonte de átomos e um laser de CO2 de alta potência e sua óptica. Demonstramos o aprisionamento de átomos de 85Rb em uma armadilha magnética e magneto-óptica e analisamos sua dinâmica, obtendo resultados das taxas de perdas provocadas por colisões entre átomos aprisionados e átomos quentes provenientes do vapor de fundo e do getter. Este entendimento será importante na implementação da técnica totalmente óptica de aprisionamento simultâneo de átomos de Rb e moléculas de Rb2. / In this work we present the construction of an optical dipole trap using a CO2 laser, which involves the use of news and modern technologies never utilized by our group up to now. We have builded a new trap chamber with large optical access, used atomic dispensers as an atomic source and a high power CO2 laser and its optical components. We have demonstrated trapping and cooling of 85 Rb in a magneto-optical trap as well as and magnetic trap. By analyze its dynamic, we have obtained results on the collisional loss rates between trapped atoms imprisoned and hot atoms originating from the background gas. This understanding will be important in the implementation of the technical one entirely optical trap for Rb atoms as well as Rb2 molecules.

Estuda-se o transporte de portadores de carga no interior de um isolante dotado de centros profundos de retenção de carga. Supõe-se que os portadores tenham sido depositados na superfície livre do isolante por meio de uma descarga corona rápida e que ai a densidade superficial de carga decaia exponencialmente. Para obter-se o campo elétrico E = E (x,t) no interior do isolante. Integra-se essa equação pelo método das características e obtêm-se expressões analíticas para as linhas de corrente x = x (t,te) (te, designando o tempo de saída da carga da superfície) e para o campo elétrico E = E (t,te) ao longo de cada uma das linhas. São apresentadas famílias de curvas x = x(t,te) e de E = E(t,te),. Eliminando-se graficamente te entre as duas famílias, obtem-se a família de curvas E = E(x) parametrizada em t. Usou-se planímetro para determinar a área debaixo de cada curva E = E(x), e com isso constrói-se a curva de decaimento de potencial / The transport of charge carriers in presence of bulk traps inside an insulator. It is supposed that the carriers were deposited on the surface by a pulse of charge decaying thereafter exponentially with the time. In order to find the electric fielhd electric field E(x,t), the method of characteristics is employed, taking as parameter the time te when the leaves the surface; and ththeir position X=(t,te) and the electric field E=E(x,te) are obtained. By graphicall eliminatination, curves of E(x) are obtained for various times t. A planimeter was used to find the potential at every time as a function of the time

Foram estudas as espécies de Anastrepha coletadas pelo Servicio Nacional de Calidad y Sanidad Vegetal y de Semilla (SENAVE), no município de Concepción, estado de Concepción e no município de Santa Rosa, estado de Misiones. As moscas-das-frutas foram coletadas em armadilhas tipo McPhail com proteína hidrolisada (atraente alimentar), por um ano (maio de 2008 a maio de 2009). Foram coletadas 3.095 fêmeas de Anastrepha, pertencentes a 18 espécies: A. amita Zucchi, 1978; A. daciformis Bezzi, 1909; A. dissimilis Stone, 1942; A. elegans Blanchard, 1937; A. fraterculus (Wied., 1830); A. grandis (Macquart, 1846); A. montei Lima, 1934; A. nascimentoi Zucchi, 1978; A. pickeli Lima, 1934; A. punctata Hendel, 1914; A. serpentina (Wied., 1830); A. striata Schiner, 1868; A. sororcula Zucchi, 1978; A. turpiniae Stone, 1942; A. undosa Stone, 1942 e A. zernyi Lima, 1934, além de duas prováveis novas espécies. Oito espécies, Anastrepha amita, A. dissimilis, A. nascimentoi, A. pickeli, A. serpentina, A. striata, A. turpiniae e A. zernyi, estão sendo registradas pela primeira vez no Paraguai. Anastrepha fraterculus foi a espécie mais frequente (70,76%), seguida por A. punctata (11,11%), A. sororcula (9,73%) e A. pickeli (3,20%). As demais espécies apresentaram uma frequência inferior a 2%. Em Concepción, foram coletadas 1.273 fêmeas que correspondem a 13 espécies. Em Santa Rosa, foram capturadas 1.822 fêmeas pertencentes a 11 espécies. Sete espécies, A. montei, A. pickeli, A. serpentina, A. turpiniae, A. undosa e as duas prováveis novas espécies foram coletadas apenas em Concepción e outras cinco espécies, A. amita, A. daciformis, A. elegans, A. grandis e A. zernyi, foram capturadas somente em Santa Rosa. As espécies comuns para os dois municípios são A. dissimilis, A. fraterculus, A. nascimentoi, A. punctata, A. striata e A. sororcula. Dez espécies estavam registradas no Paraguai, mas considerando os dados aqui apresentados, 20 espécies são conhecidas atualmente no Paraguai. Alguns parâmetros faunísticos foram analisados e uma chave ilustrada para todas as espécies registradas no Paraguai foi elaborada. / Species of Anastrepha surveyed by Servicio Nacional de Calidad y Sanidad Vegetal y de Semilla SENAVE in counties of Concepción, state of Concepción, and in Santa Rosa, state of Missiones, were studied. Fruit flies were collected in traps MacPhail type baited with hidrolised protein throughout one year (from May 2008 to May 2009). In both counties were collected 3,095 females of Anastrepha belonging to A. amita Zucchi, 1978; A. daciformis Bezzi, 1909; A. dissimilis Stone, 1942; A. elegans Blanchard, 1937; A. fraterculus (Wied., 1830); A. grandis (Mcquart, 1846); A. montei Lima, 1934; A. nascimentoi Zucchi, 1978; A. pickeli Lima, 1934; A. punctata Hendel, 1914; A. serpentina (Wied., 1830); A. sororcula Zucchi, 1978; A. striata Schiner, 1868; A. turpiniae Stone, 1942; A. undosa Stone, 1942 and A. zernyi Lima, 1934, besides two probable new species. Eight species are being recorded for the first time in Paraguay such as Anastrepha amita, A. dissimilis, A. nascimentoi, A. pickeli, A. serpentina, A. striata, A. turpiniae and A. zernyi. Anastrepha fraterculus (70.76%) was the most frequent species, followed by A. punctata (11.11%), A. sororcula (9.73%) and A. pickeli (3.20%). Frequency of the other species was less than 2%. In Concepción, 1,273 females were collected belonging to 13 species and, in Santa Rosa were collected 1,822 females distributed in 11 species. Seven species, A. montei, A. pickeli, A. serpentina, A. turpiniae, A. undosa and two probable new species were collected only in Concepción and other five species, A. amita, A. daciformis, A. elegans, A. grandis and A. zernyi were captured only in Santa Rosa. Species more common in both counties were A. dissimilis, A. fraterculus; A. nascimentoi, A. punctata, A. strita and A. sororcula. Ten species were previously known in Paraguay, but considering the records herein presented, 20 species are currently recorded in Paraguay. Some faunistic parameters were studied and an illustrated key for all species recorded in Paraguay was elaborated.

A taxa de infecção mínima (TIM) em flebotomíneos é uma informação útil para estudos epidemiológicos em leishmaniose. Quando estes estudos de campo contem grande número de insetos, a PCR é a indicada para caracterização por Leishmania nos vetores. Este estudo avaliou a PCR na identificação da (TIM) natural por Leishmania spp. em Lutzomyia longipalpis e, ao mesmo tempo, determinou as (TIM) por Leishmania spp em uma micro-região endêmica do Estado de São Paulo. Na primeira parte deste estudo, as avaliações do desempenho das PCRs convencional (cPCR) e em tempo real (qPCR) foram realizadas em 66 amostras de conteúdo intestinal de flebotomíneos utilizados no xenodiagnóstico (30 positivas e 36 negativas). O material contido nas lâminas foi transferido para tubos com solução salina estéril e congeladas a -20° C por cerca de 12 meses. Os marcadores moleculares utilizados foram RV1/RV2 para L. (L.) infantum na cPCR; e Linj31 para sub gênero (L.) (Leishmania) na qPCR. Das 30 amostras positivas, 20 (67%) e 21 (70%) foram positivas utilizando os marcadores RV1/RV2 e Linj31, respectivamente. Das 36 amostras negativas no xenodiagnóstico, 2 (5%) foram positivas em todos os marcadores moleculares. Na segunda parte foram analisados insetos capturados durante 2 a 3 noites/mês durante 11 meses (janeiro a novembro de 2012) usando 10 armadilhas automáticas de luz do tipo CDC ao redor de um canil em uma transição entre bairro periurbano e urbano de Dracena. As áreas de captura foram agrupadas em 3 zonas para determinar a TIM. Um total de 1.690 Lu. longipalpis foram capturadas durante o período estudado. Destes, 292 (17,25%) eram fêmeas de flebotomíneos e foram agrupadas em 165 pools (1 a 5 insetos) para extração de DNA e análise por PCR. Resultados positivos para L. (L.) infantum na cPCR e qPCR foram vistos em 7,28% (12/165) e 4,85% (8/165) das amostras, respectivamente. Estes dados confirmam que espécimes capturados na área de estudo estavam infectados por L. (L.) infantum. A TIM durante os 11 meses de capturas foi de 4,10% (292 fêmeas coletadas). Os ecótopos com TIM mais altos foram canil, galinheiro e casa 2. Flebotomíneos infectados estavam presentes nos locais de captura com abundância de hospedeiros. O maior número de pools positivos (6/93) foi obtido no galinheiro, todavia a maior TIM foi obtido em um domícilio (1/6) 16,67%. / The minimum infection rate (MIR) in sandflies is a useful information for epidemiological studies on leishmaniasis. When these field studies consider large numbers of insects, PCR is indicated for identification and characterization of Leishmania in the vectors. This study evaluated a PCR in the identification of natural (MIR) by Leishmania spp. in Lutzomyia longipalpis and, at the same time, determined MIR by Leishmania spp in a micro region endemic in São Paulo State . In the first part of this study, the performance evaluation of conventional PCR (cPCR) and real-time PCR (qPCR) were carried out on 66 intestinal contents samples of non-xenodiagnostic sandflies (30 positive and 36 negative). The material contained in the slides was transferred to tubes with sterile saline solution and frozen at -20 ° C for about 12 months. The molecular markers used were RV1 / RV2 for L. (L.) infantum in cPCR; E Linj31 for sub genus (L.) Leishmania on qPCR. From the 30 positive samples, 20 (67%) and 21 (70%) were positive using the RV1 / RV2 and Linj31 markers, respectively. From the 36 negative xenodiagnostic samples, 2 (5%) were positive in all molecular markers. In the second part, we analyzed insects captured during 2 to 3 nights / month for 11 months (January to November 2012) using 10 CDC automatic light traps around a kennel in a transition between urban and suburb of Dracena. Capture areas were grouped into 3 zones to determine MIR. A total of 1,690 Lu. longipalpis were captured during the study period. From these, 292 (17.25%) were female sand flies and were grouped into 165 pools (1 to 5 insects) for DNA extraction and PCR analysis. Positive results for L. (L.) infantum in cPCR and qPCR were seen in 7.28% (12/165) and 4.85% (8/165) of the samples, respectively. These data confirm that the specimens captured in the study area were infected by L. (L.) infantum. The MIR during the 11 months of captures was 4.10% (292 females collected). The highest MIR ecotopes were kennel, chicken coop and house 2. Infected sandflies were presented at capture sites with host abundance. The highest number of positive pools (6/93) was obtained in henhouse, however the highest MIR was obtained in a domicile (1/6) 16.67%.

O presente trabalho visou analisar padrões de atividade e uso de habitats por mamíferos de médio e grande porte, bem como dieta e sobreposição de nicho trófico de espécies de felinos e canídeos, numa região fragmentada do estado de São Paulo. Na paisagem estudada, existem duas unidades de conservação de proteção integral com vegetação de cerrado e floresta semidecídua, além de fragmentos de floresta nativa (semidecídua) em propriedades privadas. As hipóteses gerais do trabalho são: em ambientes mais impactados, i. as espécies de mamíferos de médio e grande porte tendem a generalizar seu comportamento de uso de habitat e padrão de atividade e ii. predadores de topo de cadeia alimentar aumentam a competição por recursos alimentares. Para explorá-las, foram estudados, por meio de armadilhas fotográficas e triagem de fezes, os seguintes aspectos: a) a freqüência do uso de diferentes habitats por mamíferos de médio e grande porte; b) o padrão de atividade de mamíferos de médio e grande porte; c) a dieta e a sobreposição de nicho de três carnívoros de topo de cadeia alimentar: lobo-guará (Chrysocyon brachyurus), onça-parda (Puma concolor) e jaguatirica (Leopardus pardalis). As coletas foram distribuídas em sete fragmentos, onde existem fitofisionomias nativas - cerrado sensu stricto, cerradão e floresta semidecídua - e também reflorestamento com espécies de eucaliptos. Foram obtidas 165, fotografias, nas quais identificou-se 17 espécies. Foram coletadas e identificadas 233 amostras de fezes, sendo 93 de lobo-guará, 68 de onça-parda, 38 de jaguatirica, 30 de outros pequenos felinos e 4 de cachorro-do-mato. Os resultados mostraram que, de forma geral, os mamíferos de médio e grande porte utilizam a área como um todo; os mamíferos mais especialistas, como o tapiti (Sylvilagus brasiliensis), mantiveram sua preferência por um habitat específico. Testes de correlação de Spearman mostraram que algumas espécies mais suscetíveis a alterações antrópicas mostraram-se correlacionadas a áreas com maior tamanho e grau de conectividade. Em relação aos padrões de atividade, os dados indicam que as espécies estão generalizando o seu comportamento: espécies que tinham atividade em alguns períodos do dia estão permanecendo ativas também em outros períodos. Quanto à dieta, o lobo-guará foi a espécie que utilizou mais itens entre os carnívoros estudados, alimentando-se de aves, répteis, frutos, mamíferos de diversos portes e insetos. A onça-parda e a jaguatirica apresentaram uma dieta mais restrita, sendo que os mamíferos representaram 90% dos itens consumidos. Houve uma alta sobreposição de nicho trófico entre lobo-guará e jaguatirica, indicando competição entre essas espécies. Os resultados, obtidos tanto por meio de armadilhamento fotográfico como por análise da dieta, indicam que pode existir uma relação entre áreas com maior grau de conservação (áreas maiores, menos isoladas estruturalmente e imersas em matrizes mais permeáveis) e a freqüência de mamíferos, a sobreposição de nicho dos carnívoros de topo e a densidade de fezes encontradas / The following study analyzed activity patterns and habitat use of large and medium size mammals as well as diet and trophic niche overlapping of feline and canid species in a fragmented area of the State of São Paulo. The landscape studied contains two fully protected conservation units with cerrado and semi-deciduous vegetation and also remnants of native semi-deciduous forest located in private properties. The general hypothesis of this study are: in more impacted environments, i, large and medium size mammal species tend to generalize their behavior regarding habitat use and activity patterns and ii, top food chain predators increase the competition for resources. The following aspects were studied through photographic traps and fecal sorting: a) frequency of different habitat use by large and medium size mammals; b) activity pattern of large and medium size mammals; c) diet and niche overlapping of three top food chain carnivores: Chrysocyon brachyurus, Puma concolor and Leopardus pardalis. Samples were withdrawn from seven fragments of native phytophysiognomies - cerrado sensu stricto, cerradão and semideciduous forest - and from areas of eucalyptus plantations. One hundred and sixty five photographs were obtained, where 17 species were identified. Two hundred and thirty three samples of feces were collected and identified, of which 93 of Chrysocyon brachyurus, 68 of Puma concolor, 38 of Leopardus pardalis, 30 of other small felines and 4 of Cerdocyon thous. The results show that, generally, large and medium size mammals use the entire area. However, more specialist mammals, such as the Sylvilagus brasiliensis, kept their preference for a more specific habitat. Spearman correlation tests demonstrated that those species which are more susceptible to anthropic alterations were more correlated with areas containing a higher connectivity and bigger size. The data also indicated that species are generalizing their behavior regarding the activity patterns: species that were active in some periods of the day are now remaining active in other periods as well. Among the carnivore species studied, Chrysocyon brachyurus was the specie with the most diversified diet, feeding on birds, reptiles, fruits, insects and mammals. Puma concolor and Leopardus pardalis had more restricted diets, where 90% of the items ingested belonged to other mammals. The trophic niche of C. brachyurus and L. pardalis species were strongly overlapped, indicating competition between them. The results obtained through photographic traps and diet analysis indicate that there might be a relation between more conserved areas (less isolated larger areas immersed in more permeable matrixes) and the frequency of mammals, the overlapping niche of top food chain carnivores ad the density of feces found.

O decaimento do potencial de superfície de um isolante carregado por um pulso rápido de descarga corona é estudado supondo-se densidade finita de armadilhas profundas, o que generaliza o cálculo anterior de Rudenko. Supõe-se que uma fração da carga depositada na superfície é instantaneamente injetada, obtendo- se o potencial como função do tempo, bem como o potencial residual. O comportamento assintótico do potencial é estudado para o caso em que toda a carga da superfície é\' instantaneamente injetada. são apresentados alguns gráficos do transiente,correspondentes a particulares valores dos parâmetros que levam a expressões mais simples / The decay of the surface pontential of a sample,corona charged by a pulse, is studied. It is assumed a finite density of deep traps,and this makes our calculation a generalization of previous work by Rudenko. It is supposed that a fraction of the charge deposited on the surface moves inside the sample and the potential as a function of the time is obtained as well as the residual potential. The asymptotic behavior of the potential is also obtained when alI the charge is injected. Those transients leading to simples mathematical expressions are shown in graphs